With the increasing use of unitized and complex aerospace structures, there is a critical need for technologies that allow for Non-Destructive Inspection (NDI) in locations of the structure that are not easily accessible. Limited Access NDI (LANDI) is an emerging field of interest being pioneered to support programs such as Sea Launch, and the Boeing 787 aircraft. Utilizing innovative LANDI approaches, ultrasonic, visual, and x-ray techniques, among others, can be applied to composite and metal aircraft sub-structure.
X-ray inspection methods are often the most suitable for certain structures, due to the type or size of defects or damage that must be found, or the nature of the structure or material under inspection. The problem is that interpretation of the x-ray data taken in a limited access area (such as a hat stiffener on the 787 fuselage) is very difficult because the area cannot be seen with the naked eye or traditional cameras.
A capability of providing visual information that directly correlates to the x-ray data would provide several key advantages. Precise visual information is extremely advantageous when determining the location, size, and shape of defects or damage. Many features on an x-ray image may be mis-identified as defects or damage, but may simply be surface features due to manufacturing processes or foreign objects. The depth of the feature on an x-ray image may require multiple shots, using parallax principles. However, visual inspection of the area would often eliminate the need for multiple shots (also reducing x-ray exposure), if the feature is actually on the surface.
There are no techniques currently in existence that correlate x-ray data with visual information to achieve the advantages listed above. Optical borescopes exist that can provide remote visual inspection within structures. However, even if they were to be attached to an x-ray detector to provide visual information, there would be no adequate way to directly correlate the visual and x-ray images. Positioning of cameras that might provide better correlation is not possible for limited access areas, due to limited head space.